Hardcore players in general (but not all of them) can give casual players a hard time, especially because hardcore players who look down on casuals will tend to say so, whereas hardcore players who respect casual players rarely have any incentive or opportunity to stick up for them (outside of puerile ass-kissing).
Most of the attitude is unjustified. But also there are some times when players are trying to talk about something about advanced play, and the discussion can get side-tracked when weaker players who lack a similar level of expertise start making claims as if they're on the same level. There's absolutely nothing wrong with someone contributing to a discussion per se, no matter their level, but it can get frustrating when that player assumes that their contribution is of equal value just because. It MAY be useful or interesting, but there is a higher chance that it is not very helpful than something put forward by a better player.
The reason one player is better than another is almost always because the better player fundamentally understands some things about the fight better than the weaker player. Reactions come into play, but all other aspects, including reads, strategy etc. are based on the player's understanding of how to play the game.
Understanding =/= knowledge by the way. There is a lot more to the game than frames and spacing. But there are no (or mostly negligible) physical limitations to playing - it doesn't help being faster, or stronger, or better at controlling the pad. Playing the game is all about choices, and players who understand the game better will, over the course of a fight, MM, tournament or whatever, make better choices that give them a better chance of winning.
But the attitude is often completely unjustified. For a start, where do you draw the line between casual and pro? Many players who've looked up some frame data think they are on the elite level. Many players on this site think they are an expert player, in a group with players on their level or better, and anyone below them is not. So you end up with players who think they know the game better than they actually do, and more often than not it is these players who dismiss weaker players as casual players whose input doesn't matter.
Anyway, all this aside, I don't get why this thread is here. To those defectors: if you've moved on, move on! I am pretty tired of the 100s of daily posts which include the words "I quit the game some time ago, but...". Just quit and leave, or man up and accept that you like the game and are playing it. If you're not playing it, why are you trolling these forums?